1. Field of the Invention
The present invention relates generally to a method and apparatus for adjusting a gap. More particularly, the present invention relates to a method and apparatus for adjusting a gap in a printer.
2. Description of the Related Art
Many types of printers, such as impact printers, contain a print head used to print on printable media, such as paper. The print head of an impact printer contains one or more printing elements that strike, either directly or indirectly, the printable media to produce the printed document. In one example, the printer element may strike the printable media through an ink ribbon. In this example, the printer element that strikes the printable media may be one of a plurality of needles that are driven by one or more electric solenoids or coils. Also, impact print heads may be able to move from one side of the impact printer to the other along a transport shaft, thereby allowing the impact print head to strike at different portions along the width of the printable media.
Examples of impact printers include dot matrix printers and character printers. Point of sale printers are another example of an impact printer. Point of sale printers may require the use of impact print heads because users of point of sale printers may use multi-part forms.
In order to print correctly, impact printers require tight control of the gap between the print head and a platen. Printable media passes through the gap, which is defined by the print head and the platen. In one example, maximum tolerance for error in the distance of the gap may be held to +/−0.0008 inches or +/−0.02 millimeters. Also, the gap may need to be controlled at all print positions as the print head travels across the printable media. The correct distance for the gap may depend on the thickness of the printable media onto which the print head prints. Failure to correctly adjust the gap can result in misalignment or jamming of the printable media and premature failure of the print head.
Achieving a tight gap tolerance may present considerable challenges. For example, a high level of skill, such as that provided only by skilled technicians, may be required on a manufacturing line during assembly of the printer. A high level of skill may also be required in repairing the printer, such as when the print head must be replaced. However, requiring high levels of skill to adjust the gap makes gap adjustment inaccessible to a layperson, and requires a printer user to waste both time and money obtaining technicians having sufficient levels of skill in printer technology.
In existing designs, the gap can vary depending on the amount of force used to position the print head during adjustment. This force may be provided by a user in a non-uniform fashion, thereby leading to intolerable error in adjusting the gap distance. In existing designs, the gap can also vary depending on how consistently the user performing the adjustment can feel when the correct gap has been achieved. These existing designs also fail to minimize clearances between components of the printer. Such clearances may lead, individually or cumulatively, to error in the gap distance.